Cylindrical optical data memory

ABSTRACT

A data storage medium includes an optical information carrier comprising a spiral-wound polymer film. The central area of the data storage medium is provided with a recess whose periphery is formed by the innermost winding of the polymer film.

This application is the U.S. national phase of international applicationPCT/EP00/04675 filed May 23, 2000 which designated the U.S.

BACKGROUND AND SUMMARY

The invention relates to a data storage medium having an opticalinformation carrier which comprises a spiral-wound polymer film.

DE-298 16 802 describes a data storage medium having an informationcarrier, wound in a plurality of plies onto a winding core in a spiralfashion, for optically readable information units. The informationcarrier may comprise a polymer film, with an adhesion layer beinglocated between each pair of adjacent plies. Information can be writtento this data storage medium by locally heating the polymer film by meansof a write beam of a data drive, as a result of which the refractiveindex and thus the reflecting power (reflectivity) change locally at theinterface of the polymer film. This may be detected by means of a readbeam in the data drive. By focussing the write beam or read beam,information may be specifically written to or read from a preselectedply of the information carrier. The winding core may be opticallytransparent and may have a recess in its central area that serves toaccommodate the read/write device of a data drive. The read/write deviceis moved relative to the data storage medium, while the data storagemedium is stationary, so that the data storage medium need not bebalanced to take account of a rapid rotational motion.

In the existing data storage medium, the winding core is a disruptivefactor, since its optical quality is inadequate unless it ismanufactured with a high degree of elaborateness. Since, when the datastorage medium is used in a data drive whose read/write device issituated in the recess of the winding core, the winding core is requiredto transmit a beam a number of times during each read operation,inadequate optical quality has particularly unfavorable consequences.

It is an object of the invention to improve the existing data storagemedium such that no problems arise as a consequence of inadequateoptical quality of a winding core and yet the data storage medium can bemanufactured economically.

This object is achieved by means of a data storage medium having thefeatures of claim 1. Claim 7 specifies a process for producing a datastorage medium of this kind. Claim 9 relates to the use of such a datastorage medium in a drive that is attuned to it. Advantageousembodiments of the invention follow from the dependent claims.

The data storage medium of the invention has an optical informationcarrier which comprises a spiral-wound polymer film. The central area ofthe data storage medium is provided with a recess whose periphery isformed by the innermost winding of the polymer film. Accordingly, thedata storage medium contains no separate winding core such as is thecase with the existing data storage medium.

The reading of information or data from the data storage medium of theinvention and—if the data storage medium is set up for the input of databy the user—the writing of information to the data storage medium istherefore not hindered by a winding core. Accordingly, the data storagemedium of the invention is particularly suitable for use in a drive inwhich a read device and an optional write device are arranged in therecess in the central area of the data storage medium.

Preferably, the polymer film is wound in a plurality of polymer filmplies through which information can be read from a preselected polymerfilm ply and, optionally, can be written to a preselected polymer filmply. There may be an adhesion layer between each pair of adjacentpolymer film plies in order to fix the polymer film plies to oneanother. For example, from 10 to 30 polymer film plies may be wound atopone another, or else a greater or lesser number. At a polymer filmthickness of between 10 μm and 100 μm, preferably below 50 μm or around35 μm, the information on different polymer film plies can be separatedfrom one another with good resolution by means, for example, ofread/write devices which are known from DVD technology. An adhesionlayer may, for example, have a thickness in the range between 1 μm and40 μm, preferably below 25 μA or around 2 μm. A suitable adhesion agentcomprises, for example, an acrylate adhesive which is free from airbubbles and which is crosslinked, for example, chemically or byirradiation with UV or electron beams. With a multi-ply data storagemedium construction of this kind, it is possible to achieve a very highstorage density. Furthermore, even without a winding core, themechanical stability is sufficient and may be increased further, forexample, by inserting the data storage medium into an outer sleeve.Slight deviations of the wound polymer film from an ideal spiral form,such as might arise, for example, in the absence of a winding core bydeformation of the windings of the polymer film, are not disruptive tothe reading and/or writing of data; since the focus of a read beamand/or of a write beam may be tracked without any problems in order toremain in a preselected ply of the information carrier. If the readdevice and the optional write device are disposed in the recess in thecentral area of the data storage medium and are moved relative to thedata storage medium in order to read and/or write information, while thedata storage medium is stationary, even any possible imbalance in thedata storage medium is irrelevant.

Preferably, the refractive index of the adhesion layer differs onlyslightly from the refractive index of the polymer film, in order tominimize disruptive reflections of the read beam or of the write beam ata boundary between a polymer film ply and an adjacent adhesion layer. Itis particularly advantageous if the difference in the refractive indicesis less than 0.005. Any difference in the refractive indices may,however, be utilized for the purpose of formatting the data storagemedium.

In one preferred embodiment of the data storage medium of the invention,the refractive index of the polymer film can be changed locally byheating. Suitable material for the polymer film comprises, for example,polymethyl methacrylate (PMMA) or biaxially oriented polypropylene(BOPP). If polypropylene, following extrusion to the film, ispretensioned in two planes, a high inherent energy is stored in thematerial. In the case of local heating, by means of a write beam, forexample, there is a severe change in the material by reformation, andthis is so even when a relatively small amount of energy is depositedper unit area. In this way it is possible, for example, to achieve achange in refractive index of approximately 0.2 over an area for onestored information unit with a diameter or side length of approximately1 μm, and this is readily detectable by means of a read beam.

The polymer film may be assigned an absorber which is set up at leastpartly to absorb a write beam and to emit the generated heat at leastpartly, locally, to the polymer film. The absorber comprises, forexample, dye molecules which are present in the polymer film or in anadhesion layer adjacent to the polymer film, and permits local heatingof the polymer film, sufficient to change the refractive index, for arelatively low write beam intensity.

The data storage medium of the invention may be produced by winding thepolymer film spirally onto a winding body and subsequently withdrawingthe winding body from the central area of the data storage medium. Ifthere is to be an adhesion layer between each pair of adjacent polymerfilm plies, then in one advantageous embodiment of the process thepolymer film is provided on one side with an adhesion layer which facesoutward when the polymer film is wound onto the winding body. Theadhesion layer is therefore unable to bond to the winding body, so thatat the end of the winding operation the winding body can be withdrawnwithout any problems from the central area of the data storage medium.When the winding operation has been concluded, the outward-facingadhesion layer on the outermost polymer film ply may be covered with anadditional, nonadhering material ply or else, for example, may beremoved by means of a solvent or rendered nonadhesive by chemical orphysical treatment. In this way, a data storage medium of the inventioncan be produced economically.

BRIEF DESCRIPTION OF THE DRAWINGS

In the text below, the invention is elucidated further with reference toembodiment examples. The drawings show, in

FIG. 1, a data storage medium of the invention which comprises aspiral-wound polymer film, in diagrammatic perspective representation,parts of a drive attuned to the data storage medium being arranged in arecess in the central area of the data storage medium;

FIG. 2, a diagrammatic side view of a process step in the production ofa data storage medium of the invention,

FIG. 3, a diagrammatic cross section through the central area of a datastorage medium of the invention, and

FIG. 4, a diagrammatic cross section through the central area of a datastorage medium of the invention in the course of a process stepaccording to another embodiment of the production process.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows in diagrammatic representation a data storage medium 1 anda read/write device 2 of a drive attuned to the data storage medium 1.The data storage medium 1 comprises a number of plies 10 of a polymerfilm 11 which serves as information carrier and is wound spirally. Thedesign of the central area of the data storage medium 1 is described inmore detail later on with reference to FIG. 3. For ease of illustration,the individual plies 10 of the polymer film 11 have been shown in FIG. 1as concentric rings, although the plies 10 were formed by spiral windingof the polymer film 11. Between each pair of adjacent plies 10 of thepolymer film 11 there is an adhesion layer 12. For reasons of clarity,the adhesion layers 12 have been drawn in FIG. 1 in an increasedthickness which is not to scale.

In the embodiment example, the polymer film 11 consists of biaxiallyoriented polypropylene and has been pretensioned in both surfacedirections prior to winding. In the embodiment example, the polymer film11 has a thickness of 35 μm; other thicknesses in the range from 10 μmto 100 μm or even thicknesses lying outside of this range are likewiseconceivable. The adhesion layers 12 are free from gas bubbles and in theembodiment example consist of acrylate adhesive, to which an absorberdye has been admixed, at a thickness of 23 μm, preferred layerthicknesses being between 1 μm and 40 μm. In the embodiment example, thedata storage medium 1 contains twenty plies 10 of the polymer film 11and has an external diameter of approximately 30 mm. Its height is 19mm. A different number of plies 10, or different dimensions, arelikewise possible. The number of windings or plies 10 may, for example,be between ten and thirty, or else may be greater than thirty.

The read/write device 2 arranged in a recess in the central area of thedata storage medium 1 comprises a read/write head 20 which can be movedbackward and forward axially and rotated in the directions of the arrowsthat have been drawn in, by means of a mechanism 21. The read/write head20 has optical elements by means of which a light beam (of wavelength,for example, 630 nm or 532 nm) produced by a laser, which is not shownin FIG. 1, may be focussed onto the individual plies 10 of the polymerfilm 11. Since the read/write head 20 is moved by means of the mechanism21, it is able to scan fully all plies 10 of the data storage medium 1.In the embodiment example, the data storage medium 1 is stationary.Consequently, it does not need to be balanced to take account of a highrotational speed (and also need not be unwound or rewound), unlike theread/write head 20. For the sake of clarity, the elements provided forbalancing the read/write head 20 have not been shown in FIG. 1. Thelaser mentioned is located outside of the read/write head 20 and isstationary; the laser beam is guided into the read/write head 20 viaoptical elements.

In the embodiment example, the laser is operated with a beam power ofapproximately 1 mW for the purpose of storing or writing information tothe data storage medium 1. The laser beam serves here as a write beamand is focussed onto a preselected ply 10 of the polymer film 11, insuch a way that the beam spot is smaller than 1 μm, the light energybeing introduced in the form of short pulses of approximately 10 μs induration. The energy of the write beam is absorbed in the beam spot,promoted by the absorber in the adjacent adhesion layer 12, leading to alocal heating of the polymer film 11 and thus to a local change in therefractive index and in the reflectivity.

In order to read stored information from the data storage medium 1, thelaser is operated in continuous wave mode (CW mode). The read beamfocussed onto the desired site is reflected as a function of the storedinformation, and the intensity of the reflected beam is detected by adetector in the read/write device 2.

The data storage medium may also be of an embodiment which cannot bewritten by the user. In this case, it contains information units writtenby the manufacturer. In this case, there is no need for a write functionin the user's data drive.

In the polymer film 11, the information units are formed by changing theoptical properties in a region having a preferred size of less than 1μm. The information may be stored in binary form; i.e., the localreflectivity adopts only two values at the site of one information unit.In other words, if the reflectivity is above a fixed threshold value, a“1”, for example, is stored at the site in question on the informationcarrier, and, if it is below this threshold value or below a different,lower threshold value, a “0” is correspondingly stored. It is, however,also conceivable for the information to be stored in a plurality of graystages. This is possible if the reflectivity of the polymer film at thesite of an information unit can be changed specifically by definedadjustment of the refractive index without saturation being reached.

FIG. 2 illustrates a process step during the production of the datastorage medium 1. The starting material is a polymer film made ofbiaxially oriented polypropylene, which is designated 30 here. On oneside, the polymer film 30 has been provided with an adhesion layer 32 ofacrylate adhesive. In order to produce the spirallike structure of theinformation carrier, the polymer film 30 is laid against a cylindricalwinding body 34, whose cross section can be seen in FIG. 2. The adhesionlayer 32 faces outward. The winding body 34 is then rotated until thepolymer film 30 has been wound up fully with the adhesion layer 32. Thisproduces the plies—designated 10 in FIG. 1—of the polymer film 30, withthe adhesion layer 32 forming the respective adhesion layers 12 betweeneach pair of adjacent polymer film plies 10. Finally, the winding body34 is withdrawn in the axial direction. Since the adhesion layer 32faces outward during winding, there is no adhesion agent between thesurface of the winding body 34 and the innermost winding of the polymerfilm 30; otherwise, the withdrawal of the winding body 34 would be mademore difficult.

FIG. 3 shows the central area of the data storage medium 1 in adiagrammatic cross-sectional view. The two inner windings of the polymerfilm 30 are shown, with the adhesion layer 32. For ease of illustration,the thicknesses of the polymer film 30 and of the adhesion layer 2 havebeen drawn in excessively large in comparison to the diameter of theinner windings, and this applies in a similar way to FIG. 2 as well.Following the withdrawal of the winding body 34, a recess 36 is formedin the central region of the data storage medium 1, the periphery 37 ofsaid recess 36 being formed by the innermost winding 38 of the polymerfilm 30. Accordingly, when the data storage medium 1 is used, there is,as illustrated by FIG. 1, no disruption by a winding core which wouldotherwise have to be penetrated once by a write beam emitted by theread/write device 2 and twice, indeed, by a read beam emitted by theread/write device 2 and received following reflection. Furthermore, atthe periphery 37 there is no adhesion material, which might, forexample, have a tendency to become soiled.

When the polymer film 30 has been fully wound, the adhesion layer 32 onthe outside of the outermost winding may be removed or covered, wherenecessary. It is also conceivable to insert the finished wound body intoa sleeve in order to achieve better stability.

The form of the inner windings of the polymer film 30 as shown in FIG. 3results when the film is wound onto the cylindrical winding body 34 (seeFIG. 2). The fact that this form does not correspond to the course of anideal spiral is a result of the fact that, at the beginning of thesecond winding, the polymer film 30 has to be displaced radially outwardin a more or less abrupt way if it lies against the free end 39 of thepolymer film 30. This deformation continues outward, but affects theinner windings in particular.

Better results are achieved with a winding body 40 as depicted in FIG.4. The winding body 40 has, in cross section, a spirallike outer contour42 with a step 44 whose radial projection corresponds to the thicknessof the polymer film 30 plus the thickness of the adhesion layer 32. AsFIG. 4 illustrates, the spirallike outer contour 42 guides the startingarea of the second winding of the polymer film 30 undisruptedly beyondthe area at the free end 39 of the polymer film 30 which lies againstthe step 44, in the course of the winding operation. Otherwise, theprocess illustrated by FIG. 4 for producing a data storage medium 1proceeds in exactly the same way as the process elucidated in connectionwith FIG. 2. As previously, the representation according to FIG. 4 isalso not to scale. Following the withdrawal of the winding body 40, thewindings of the polymer film 30 run substantially as in the case of anideal spiral.

1. A process for producing a data storage medium including an opticalinformation carrier which comprises a spiral-wound polymer film, thecentral area of the data storage medium being provided with a recesswhose periphery is formed by the innermost winding of the polymer film,the process comprising spirally-winding the polymer film onto a windingbody and subsequently withdrawing the winding body from the central areaof the data storage medium.
 2. The process as claimed in claim 1,wherein the polymer film is provided on one side with an adhesion layerwhich faces outward when the polymer film is wound onto the windingbody.
 3. The process as claimed in claim 2, wherein the winding bodycomprises a spiral-like outer contour having a step portion with a sizecorresponding to the combined thickness of the polymer film and theadhesion layer.
 4. The process as claimed in claim 1, wherein thewinding body comprises a cylindrical wining body.
 5. The process asclaimed in claim 1, wherein the winding body comprises a spiral-likeouter contour.
 6. The process as claimed in claim 2, wherein thespiral-like outer contour includes a step portion.
 7. The use of thedata storage medium in a drive which is attuned to it and comprises aread device and, optionally, a write device, the read device and theoptional write device being disposed in a recess in the central area ofthe data storage medium and being moved relative to the data storagemedium, white the data storage medium is stationary, for the purpose ofreading and/or writing information, wherein the data storage mediumincludes a spirally-wound polymer film having an optical property thatcan be changed locally by heat, the central area of the data storagemedium containing no winding core so as to provide the recess, theperiphery of the recess being formed by the innermost winding of thepolymer film, wherein the data storage medium further comprises anabsorber for absorbing the heat and subsequently emitting at least partof the absorbed heat to the polymer film.
 8. A method for using a datastorage medium including an optical information carrier which comprisesa spiral-wound polymer film, the central area of the data storage mediumbeing provided with a recess whose periphery is formed by the innermostwinding of the polymer film the method comprising: disposing a readdevice having a read beam in the recess of the data storage medium; andmoving the read device while keeping the data storage medium stationaryin order to direct the read beam onto data storage medium to read datatherefrom.
 9. The method as claimed in claim 8, wherein the read deviceis part of a read/write device that also has a write beam, and themethod further comprises: moving the read/write device while keeping thedata storage medium stationary in order to direct the write beam ontothe data storage medium to write data thereto.
 10. A data storage mediumincluding a spirally-wound polymer film having an optical property thatcan be changed locally by heat, the central area of the data storagemedium being provided with a recess which contains no winding core andwhose periphery is formed by the innermost winding of the polymer film,wherein the data storage medium further comprises an absorber forabsorbing the heat and subsequently emitting at least part of theabsorbed heat to the polymer film.
 11. The data storage medium asclaimed in claim 10, wherein the polymer film is wound in a plurality ofpolymer film plies trough which information can be read from apreselected polymer film ply and, optionally, written to a preselectedpolymer film ply.
 12. The data storage medium as claimed in claim 11,wherein an adhesion layer is disposed between each pair of adjacentpolymer film plies.
 13. The data storage medium as claimed in claim 12,wherein the refractive index of the adhesion layer differs only slightlyfrom the refractive index of the polymer film.
 14. The data storagemedium as claimed in claim 10, wherein the polymer film comprisesbiaxially-oriented polypropylene.
 15. The data storage medium as claimedin claim 10, wherein the polymer film comprises polyethyl methacylate.16. A data storage medium including a spirally-wound informationcarrier, the central area of the data storage medium being provided witha recess which contains no winding core and whose periphery is formed bythe innermost winding of the information carrier wherein the informationcarrier is spirally-wound so as to provide a plurality of plies and: anadhesion layer is disposed between adjacent plies of the informationcarrier.
 17. The data storage medium as claimed in claim 16, where theinformation cater comprises a polymer film.
 18. The data storage mediumas claimed in claim 17, wherein the refractive index of the polymer filmcan be changed locally by heating.
 19. The data storage medium asclaimed in claim 17, wherein the polymer film is assigned an absorberwhich is set up at least partly to absorb a write beam and to emit thegenerated heat at least partly, locally, to the polymer film.
 20. Thedata storage medium as claimed in claim 17, wherein the polymer filmcomprises a polymer film having an optical property that can be changedlocally by heat.
 21. The data storage medium as claimed in claim 16,wherein the adhesion layer comprises acrylate adhesive.
 22. The datastorage medium as claimed in claim 16, wherein the adhesion layercomprises acrylate adhesive mixed with an absorber dye for absorbingheat.
 23. A memory device comprising: a data storage medium including aspirally-wound information carrier, the central area of the data storagemedium being provided with a recess which contains no winding core andwhose periphery is formed by the innermost winding of the informationcarrier, wherein the information carrier is spirally-wound so as toprovide a plurality of plies; and a read head provided in the recess forreading data from the spirally-wound information carrier by focusing alight beam on selected individual plies.
 24. The memory device accordingto claim 23, wherein data is read by moving the read head and keepingthe data storage medium stationary.
 25. A memory device comprising: adata storage medium including a spirally-wound information carrier, thecentral area of the data storage medium being provided with a recesswhich contains no winding core and whose periphery is formed by theinnermost winding of the information carrier, wherein the informationcarrier is spirally-wound so as to provide a plurality of plies; and aread/write head provided in the recess for reading data from and writingdata to the spirally-wound information carrier by focusing a light beamon selected individual plies.
 26. The memory device according to claim25, wherein data is read or written by moving the read/write head andkeeping the data storage medium stationary.